Wireless communications systems enable users of User Equipment (UE) to communicate with other such users via one of a number of base stations and a core network. Typically, the UEs are mobile terminals, such as cellular telephones and the like. In an active or connected state a UE is registered with the network and has a Radio Resource Control (RRC) connection with a base station so that the network knows to which base station (or cell thereof) the UE belongs and can transmit data to and receive data from the UE. The base station (i.e. the serving cell) provides mobility information and security parameters for the user equipment. The UE also establishes a default Evolved Packet System (EPS) Bearer to an endpoint beyond the base station, typically a gateway, in the Enhanced Packet Core (EPC) network, or core network for short. An EPS Bearer defines a transmission path through the network and assigns an IP address to the UE, at which it can be reached by other communication devices, such as another UE. An EPS Bearer also has a set of data transmission characteristics, such as quality of service, data rate and flow control parameters, which are defined by the subscription associated with the UE and are established by the Mobility Management Entity (MME) upon registration of the UE with the network.
The EPS Bearer is thus managed by the MME, which signals to the UE when it needs to activate, modify, or deactivate a particular EPS Bearer. Thus there are always two connections between the UE and the communication network: one for the user data transmitted using the established EPS bearer (also known as the user plane) and another one for managing the EPS Bearer itself (also known as the control plane).
As part of the Long Term Evolution (LTE) of UTRAN (UMTS Terrestrial Radio Access Network) referred to as E-UTRAN, there are plans to introduce a feature of direct device-to-device (D2D) communication when the UE can communicate user data to another UE that is within the transmission range of the first UE without the need to use LTE network resources. This direct communication would result in better utilization of the available resources, especially on the radio interface, where these are limited.